STOMATA FROM GROWTH-CHAMBER-GROWN VICIA-FABA HAVE AN ENHANCED SENSITIVITY TO CO2

Abaxial stomata from Vicia faba leaves grown in a growth chamber under constant light, temperature and humidity showed an elaborate pattern of aperture changes over the course of a light cycle. These aperture c hanges, were tightly correlated with changes in chamber COL concentrat ion (r(2)=0.83). Changes in chamber [CO2] resulted, in turn, from subs tantial daily fluctuations in ambient [CO2], typical of the Los Angele s environment, with a constant offset caused by photosynthesis and res piration of the plants within the chamber, The dominant role of the st omatal response to CO2 in the control of aperture tvas confirmed by ma nipulation of chamber [CO2]. Fast (15 min) increases and decreases in [CO2] caused rapid decreases and increases in aperture, while constant [CO2] resulted in constant aperture. In contrast, aperture changes in comparable plants grown under greenhouse conditions were tightly corr elated with changes in incident solar radiation (r(2)=0.80), and poorl y correlated with changes in [CO2] (r(2)=0.09). Greenhouse-grown plant s transferred to growth chamber conditions showed no apparent response to CO2. These data indicate that growth-chamber-grown V. faba leaves provide an experimental system optimally suited for the study of the s tomatal response to CO2, and suggest that acclimation to environmental conditions alters the sensitivity of stomata to CO2.